To develop a valid method for measuring the functional capacity of the anionic and cationic pathways for renal tubular secretion in normal volunteers. Famotidine and PAH will be used as the cationic and anionic transport markers, respectively. Iothalamate will be used as the measure of glomerular filtration rate (GFR) during the study. This pilot study will include determination of the renal tubular transport maximum (Smax), the plasma concentration at 50% of Smax (EC50) through a step-up infusion rate, & the ratio GLr/GFR for both compounds.